Analysis in the measurement of optical signal-noise-ratio degradation of an optical node

The optical signal-Noise-Ratio (OSNR) degradation (OSNRD) induced by an opt ical network node is studied in the paper. It is shown that the difference of OSNRs detected before and after the node depends not only on internal pa rameters of the optical node to be measured, but also on the external condi tion. This kind of difference can not be used to evaluate the optical perfo rmance of the node unless either gain condition or power condition is met d uring the measurement. It is also found that the relationship between OSNRD s and internal parameters of the node obtained under the two conditions are reverse. In the view of optical networking, the power condition is conside red more reasonable for the reason that the relationship between OSNRD and the node under this condition is corresponding to the case where the node i s used in optical networks.